Electron-density dependence of double-plasmon excitations in simple metals

Abstract

Double plasmons are unique fingerprints of dynamical correlations in the model of a free-electron gas beyond the random phase approximation. A combined experimental and theoretical study of double-plasmon excitations in three simple metals Na, Mg, and Al is presented. The intensities, spectral shapes, and dispersions of these excitations are analyzed as a function of momentum. The measured double-plasmon intensity is found to increase with a decreasing electron density, which is in good agreement with the expectations of strength of the correlation effects as a function of the electron gas density. The overall quantitative agreement between the experimental and the theoretical results is very good, while the remaining discrepancies may be due to higher order correlation effects and band-structure effects.

Dynamic many-body theory: Dynamics of strongly correlated Fermi fluids

“…1, dark red regions correspond to high intensity (logarithmic scale). The blue line is the position of the doubleplasmon peak obtained in the present work, red dots are experimental results[27] from inelastic X-ray scattering and green diamonds results from Green's functions calculations[27,59].…”

“…Therefore, electrons are much less challenging than 3 He and the RPA (or slightly modified versions) contain much of the relevant physics. The latter has raised new interest [26,27] in studying the dynamics of electrons at metallic densities in this (q; ω) region. Figure 6 shows the dynamic structure factor S(q; ω) obtained from the pair fluctuation theory.…”

“…From (C19) we obtain for the double-pole part of the Al Exp., Ref. [27] Th., Ref. [27] this dynamic interaction (5.8)…”

“…We have already shown in Figs. 6 the location of the double plasmon excitation and a comparison with the experimental inelastic X-ray scattering data [26,27]. The doubleplasmon is also accessible by Green's function methods [59].…”

“…In the homogeneous electron liquid the pair-excitation theory predicts plasmon damping as well as double-plasmon excitations. Experimental verification of the double-plasmon excitation in recent inelastic X-ray scattering measurements [26,27] has added new interest in studying the dynamics of electrons.…”